1. Field of the Invention
Present invention relates to a field of communication, especially to a method for a mobile set detaching from two or more communication systems that share the same equivalent route area (hereinafter referred to as ERA).
2. Description of the Related Art
In general, for the convenience of management, a service area of a mobile communication system can be divided into several different route areas (hereinafter referred to as RA) with each managed by a service node. After a mobile set is registered with a mobile communication system, it learns about the RA it locates. If a subscriber moves within the mobile communication system, when the mobile set finds out that it enters a new RA or it needs to initiate a periodical RA update process, it is necessary for this mobile set to carry out a RA update process. During the RA update process, if the service node changes, information on the mobile set will be eliminated from the original service node after it has been transferred to the new service node.
Generally, a detachment process may be performed so that: the mobile set informs the network that the mobile set no longer needs any service, or the network informs the mobile set that the network no longer offer any service for the mobile set. The mobile set may be detached either explicitly or implicitly. The explicit detachment means that either the network or the mobile set carries out the detachment process explicitly, while the implicit detachment means that the network detaches the mobile set without any notification. For instance, the system receives no message from the mobile set in a preset period of time, or an error (which can not be settled) happens to the physical link between the system and the mobile set. The process that the network detaches a mobile set may be initiated by either the service node (within the network) that offers service to the mobile set, or a home network register (hereinafter referred to as HSS) corresponding to the mobile set. After the detachment process completes, it is necessary to inform the HSS that the mobile set in state of detachment.
In general, when a mobile set moves from a service area of one mobile communication system to a service area in another new mobile communication system, the RAs of the two communication systems are different. In this case, it is necessary to perform a RA update process between the mobile set and the service node in the new mobile communication system. In addition, during this process, a series of processes may be implemented between the service node in the new mobile communication system and the original one to exchange relevant information to support the mobility of the mobile set. The two processes are necessary to be implemented once the mobile set returns the original communication system.
Now, an ERA method is adopted to effectively reduce the implementations of the process mentioned above during the mobile set switches between mobile communication systems. With this method, a RA of a mobile communication system and a RA of another mobile communication system are considered as one ERA. For the first time when a mobile set moves from a RA of a mobile communication system to a RA of another mobile communication system, the two service nodes of the two mobile communication systems exchange the relevant information on the mobile set so that the relevant information on the mobile set are saved in the service nodes of the two mobile communication systems. In this way, the fact that the mobile set moves within the ERA or enters a new mobile communication system is considered as that it moves within one RA of the same service node. Therefore, it is not necessary to perform any RA update process or corresponding information exchanging.
However, with the movement of the mobile set during the process that the mobile is detached from an equivalent route area (hereinafter referred to as ERA) shared by two or more communication systems, several available methods have no idea but support that the mobile set could be detached from only one of the communication systems. Therefore, in the case that the mobile is powered off, the service node of other communication system (but within the same ERA) learns about no relevant information yet. Thus, waste is caused to the system resource.